Power transmission hydrocarbon oil



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ULR/C 5. 5R4) Mom-om -Z. Ffl/NMAA/ United States Patent 3,544,472 POWERTRANSMISSION HYDROCARBON OIL Ulric B. Bray, Pasadena, and Morton Z.Fainman, Los Angeles, Calif., assignors to Bray Oil Company, LosAngeles, Calif., a corporation of California Filed Nov. 8, 1966, Ser.No. 592,944 Int. Cl. C09k 3/00; B01d 3/00 US. Cl. 25273 7 ClaimsABSTRACT OF THE DISCLOSURE A hydraulic oil for power transmissionparticularly suited to aeronautic service having a high flash pointcoupled with low pour point made by alkylating benzene with normalmonochlorinated hydrocarbons of 11 to 13 carbon atoms followed bydistillation of the alkylate to recover a fraction in the range of650760 F. having a viscosity of 20-30 centistokes at 100 F. and aviscosity index of 70l10.

This invention relates to a novel hydraulic oil and power transmissionoil useful particularly in aircraft and missiles, and other machineryoperating over a wide temperature range, and to the method of itsmanufacture. This novel hydraulic oil is a synthetic hydrocarbon oil ofunique chemical composition which provides physical and chemicalproperties heretofore impossible or extremely difficult and expensive toobtain with petroleum fractions. More particularly, the inventionrelates to a hydrocarbon hydraulic oil having the desired physical andchemical properties to an enhanced degree, particularly high flashpoint, high average boiling point, high thermal stability and highviscosity index in combination with a low pour point and relatively lowviscosity.

The invention is illustrated by drawings which show graphically in FIG.1 the distillation characteristics of the product and, in FIG. 2, adiagrammatic outline of the process.

In the operation of aircraft, especially at high altitudes and highspeeds over a wide range of geographic conditions, it is essential thatthe oil retain its fluidity at very low temperatures and provideadequate viscosity and lubricity at high temperatures in theneighborhood of 300 to 450 F. Also, it is highly desirable for the oilto exhibit minimum volatility at the highest operating temperatures inorder to avoid excessive losses from vaporization and to reduce thedanger of fires and explosions in the event of leakage onto hot surfacesduring operation. Thus the oil must have a high flash point.Furthermore, the oil must be extremely resistant to oxidation andcapable of operating for long periods of time at elevated temperatureswithout sludging or other changes in properties which would bedetrimental to the functioning of the hydraulic system. While missilesgenerally do not operate for a considerable length of time, neverthelessthe physical properties of the oil over a wide temperature range may beextremely critical in this service also.

The limitations of petroleum fractions employed in the production ofhydraulic fluid for advanced designs of air craft and missiles are wellknown. Attempts to solve the problems and correct the deficiencies ofsuch oils have generally been directed away from hydrocarbon oils andtoward the halogen containing oils such as the fluorine derivatives andtoward the oxygenated oils such as the esters and diesters. Besidesbeing very costly, such oils have often introduced other problems withpoor lubricity, increased density, hydrolytic and thermal instability,etc.

Treatment of petroleum oils by a combination of drastic defining,including fractionation, acid and solvent refining, and/or hydrogenation(hydrofining), either preceded or 3,544,472 Patented Dec. 1, 1970followed by coventional dewaxing, has produced oils from paraffiniccrudes with good physical properties at temperatures above 0 F. However,to obtain the pour point and fluidity at temperatures considerednecessary for military a rcraft (below 70 F. pour) and supersoniccommercial aircraft, additional dewaxing of a drastic and costly natureis required. Such deep refining and dewaxing are currently beingpracticed with relatively low viscosity oils having viscosities in therange of to 100 sec. Saybolt- Universal at 100 F. It has not yet beendemonstrated commercially that par-aflinic oils of higher viscosity canbe dewaxed to the necessary pour points required for military alrcraft.A substitute for the deep dewaxed parafiinic oils that has beenconsidered is a drastically refined naphthenic base oil from asubstantially wax-free crude. Such naphthenic oils as are available arelimited in viscosity-temperature susceptibility, showing a maximumviscosity index of about 75. Naphthenic stocks which yield oils ofhigher viscosity index contain excessive wax, making the oilsinoperative at the necessary low temperatures. An even greaterdisadvantage exhibited by the naphthenic base hydraulic fluids is theirlower boiling range and greater volatility for a given viscosity at 100F. as compared to the parafiinic oils.

The synthetic hydrocarbon oil of this invention possesses both a highviscosity index and a low pour point, and in addition shows a higherboiling range and less volatility for a given viscosity than eventheparafiinic oil. The chemical composition and methods of synthesis ofthe novel hydraulic fluid are shown hereinafter.

Many attempts have been made in the past to use various synthetichydrocarbon oils as the base component for aircraft hydraulic fluids,but none of the synthetic hydrocarbon fluids produced in the past havebeen satisfactory. Low molecular weight isobutylene polymers do not havesufiicient thermal stability and generally exhibit only fairtemperature-viscosity characteristics. The heavy residues produced inthe manufacture of gasoline alkylate (as, for example, alkylation ofisobutane with butylene using either H or HF catalyst) have also beenfound unsatisfactory. When alkylated benzene (commonly called polypropylbenzene or dodecyl benzene) became commercially available as a rawmaterial for the manufacture of water soluble detergents, it was thoughtthat the high boiling fractions from the alkylation reaction mightprovide suitable base oils for the manufacture of hydraulic fluids, butsuch residues were not found useful for this purpose. Such detergentbase hydrocarbons have been commonly produced by alkylating benzene withpolymers of propylene containing lesser amounts of ethylene and butylenepolymers. In preparation for the alkylation, the propylene polymer isfractionated to give, on the average, 10 to 14 carbon atoms permolecule, depending on the desired properties of the alkylate. Incommercial operations, the alkylation of benzene with the polypropylenefraction is conducted with the aid of either A101 or HP catalysts.

With either alkylating agent, a portion of the reaction product boilsabove the range acceptable in the water soluble detergent base. Suchresidues have been used successfully in the manufacture of secondaryplasticizers for vinyl resins, and as raw material for sulfonation toproduce oil soluble sulfonates. These heavy residues, and fractionstherefrom, exhibit fairly good thermal stability but their outstandingdeficiency as regards their use as hydraulic fluids is theirexceptionally poor viscositytemperature characteristics as illustratedby viscosity indexes generally less than zero. Also their volatility fora given viscosity is quite high and appears to be in keeping with theirlow viscosity index. Thermal stability has also been deficient.

It is generally believed that synthetic oils produced by polymerizingolefins such as butylene, consist of highly branched chain structuresand are substantially devoid of cyclic structures. Where the polymerizedolefin is used to alkylate benzene, regardless of whether the alkylationis conducted with AlCl or HF catalyst, the side chain has a branchedstructure. In the course of alkylation, it is apparent that some of theolefin polymerizes further before the alkylation actually takes place,with the result that high boiling residues are formed. It also appearsthat some of the high boiling residues are the result of poly-alkylationgiving di or tri alkyl benzenes. In any case, the side chains havehighly branched structure.

We have now discovered that functional fluids and particularlyhydrocarbon oils having the properties required in a hydraulic oil to ahigh degree can be made by a process of alkylation wherein a normal orstraight chain (linear) hydrocarbon of the paraffin series of controlledchain length is halogenated and then condensed with excess'benzene inthe presence of anhydrous aluminum chloride catalyst followed byfractionation to a selected narrow boiling range. Following thealkylation reaction, the AlCl catalyst is removed by hydrolysis andwater washing, neutralization with caustic alkali, and then recovery ofexcess benzene by distillation. Following this, a mono alkyl benzenefraction having about 16 to 19 carbon atoms and an average molecularweight of about 240 is removed by distillation to a temperature of about575 F. The ASTM distillation of this oil is shown in FIG. 1, curveNo. 1. This fraction can be. used in the manufacture of householddetergents by sulfonation and neutralization with sodium hydroxide.

The residue from the above distillation, amounting to about 10 to 30% ofthe weight of the paraffin halogenated, is characterized by thedistillation curve No. 2 in FIG. 1. Analysis by mass spectrometer showsit to consist principally of the following hydrocarbons:

Example Range Dialkyl benzenes, percent 48. 5 40-60 Dialkyl tetralin,percent 22. 3 15-25 Dialkyl diphenyl, percent 13. 9 10-15 Unidentifiedhydrocarbons, percent 15. 3 1015 topped, leaving 57.8% bottom (curve No.5), which is the desired specific narrow boiling range hydrocarbon powertransmission oil of our invention as will be described hereinafter ingreater detail. Other schemes can be employed for fractionating out thenarrow boiling cut desired for our hydraulic oil such as conventionalfractionating towers, etc.

The chemistry involved in the formation of these hydrocarbons isobscure, but it appears that hydrogen transfer between hydrocarbonsoccurs in the presence of the aluminum chloride catalyst. The powertransmission oil of our invention possesses a combination of propertiesnot heretofore found in any functional hydrocarbon fluid. It boilsentirely within the range of 650 to 760 F. and is generallycharacterized as follows:

Gravity, API-28-33 Viscosity, centistokes at 100 F.-20-30 Viscosity,centistokes at 210 F.3.8-4.9 Viscosity index-70-110 Flash point,C.O.C.above 400 F. Pour point, ASTMbelow -70 F.

In the manufacture of our new power transmission fluid, the paraflinhalide, preferably the chloride, is prepared from the normal paraflinhydrocarbon fraction boiling in the range of decane to tri-decane.Chlorination under pressure is preferred, for example, 25-50 p.s.i., andan excess of the hydrocarbon is used to avoid formation of dichlorides,trichlorides and other polychlor hydrocarbons as far as economicallyfeasible. A mol ratio of 2 to 5 mols of hydrocarbon per mol of chlorineis favorable. At least 70% of the chlorinated oil should be monochlor,usually 75-90%. The reaction is catalyzed by ultra violet light, forwhich mercury vapor lamps are suitable. During chlorination, thetemperature may rise from about F. to 250 F. by the heat of reaction.After separation of by-product HCl gas, the product can be fractionatedto recover the unchlorinated paraflin to be recycled to the chlorinationstep. It is preferred, however, to omit recovery of unchlorinatedparafiin hydrocarbon at this stage and proceed directly to thealkylation stage of the process, after which the paraflin hydrocarbon isrecovered by fractionation.

The paraffin hydrocarbon employed for chlorination will have a molecularweight in the range of about to 170, for example, 160, a boiling pointof about 340-450 F. and density of 0.74-0.75. It is conveniently derivedfrom a petroleum naphtha fraction boiling in the range of about 300 to460 F. by separation of the normal hydrocarbons, employing a molecularsieve, i.e.: porous alumino silicates and similar materials preparedespecially to adsorb selectively the normal or straight chainhydrocarbons which are then subsequently displaced, usually by steamingat elevated temperature.

The chlorinated parafiin (alkyl chloride) with or without unchlorinatedparaffin, is thoroughly dried and mixed with benzene, also dry and freeof thiophene, in the mol ratio of 2 to 5 mols benzene to 1 mol of alkylchloride. A ratio of about 1 to 1.5 volumes benzene to 1 volume of alkylchloride is satisfactory. The mixture is cooled to a temperature of30-50 F. and rapidly agitated while anhydrous AlCl is introduced. Thereaction can be promoted by saturating with HCl gas if desired and, whenthe chlorination reaction product is employed directly in the alkylationstage without paraflin separation, the HCl produced in the reaction canbe allowed to remain. The amount of AlCl required is about 2 to 10percent of the weight of alkyl chloride, 2 to 3% being elfective whensufiicient HCl is present. Addition of AlCl should be gradual to avoidexcessive temperature rise, cooling of the reaction mixture beingprovided. HCl pressure of 5 to 100 p.s.i. can be held on the reaction topromote the catalytic action of the aluminum chloride. After all AlClhas been introduced, the temperature is allowed to rise to 100 F.- F.

When the reaction is complete, a sludge layer is settled and discarded.HCl gas is removed as far as practicable and the remaining aluminumchloride catalyst is removed by washing with cold water, after which theoil product is neutralized with caustic soda solution. Excess benzene isthen distilled off and the product is fractionated by steam distillationor in vacuum to remove the unreacted parafiin hydrocarbons when presentand the monoalkylated benzene fraction. The heavier fraction boilingabove mono alkyl benzene is the source of the desired hydraulic oil(curve 2, FIG. 1).

In an alternative method of alkylation, the reaction product from thechlorination is cooled to 100-150 F. and undissolved HCl is gassed 013?.The liquid mixture of unreacted parafiin, chloroparafiin, and dissolvedHCl then passes to the alkylation stage where it is fed continuouslyinto a large excess of benzene with good agitation. Finely powdered AlCl.catalyst is fed in simultaneously in an amount of 2 to 5 percent byweight of the chlorparaffin. As before, about 2-5 mols of benzene isemployed per mole of chlorparafiin. HCl evolved in the alkylation isrecovered. After discarding sludge, the Oil layer is neutralized, waterwashed and distilled into four fractions, V12:

(1) Unreacted benzene (2) Unchlorinated paraifin (3) Alkylate16 to 19carbon atoms (curve 1, FIG. 1)

(4) Residueupwards of 19 carbon atoms (curve 2,

FIG. 1)

Fraction 1 is recycled to the alkylation stage of the process. Fraction2, completely freed of benzene, is recycled to the chlorination step ofthe process.

A typical sample of heavier alkylate made in the foregoing manner hadthe following properties:

The exceptionally low pour point of this oil, coupled with its highflash point, makes it unique for low temperature service in powertransmission machinery. Incorporation of a small amount of anantioxidant such as ditertiary butyl phenol, prevents deterioration onaging in storage and in service. Phenolic antioxidants are mostdesirable from the standpoint of color. Amounts of about 0.1% to 2% areusually suflicient. Typical antioxidants are polybutylated bisphenol Aand octylated diphenylamines, octyl and nonyl phenols, alkylphenolethers (Tenox BHA), and zinc dialkyl dithiophosphate (Paranox l4) and2,6-ditertiarybutyl paracresol (Parabar 441). Other additives, rustinhibtors, antifoam agents (silicones) and extreme pressure agents canbe incorporated in the oil in amounts suflicient for the purposedesired. Tricresyl phosphate in the amount of 0.2 to 2% is sometimesadded to increase lubricity of the oil and decrease wear.

All hydrocarbon oils undergo deterioration when held for prolongedperiods of time at high temperatures, above about 400 F. Although ourlinear alkylate oils are unusually stable at high temperatures, we havediscovered that certain less stable constituents thereof can be removedby reacting them with S Inasmuch as these alkylates are aromatic innature, it would be expected that S0 would efiect complete sulfonationand destruction of the oil in accord with the classical reaction:

However, we have discovered that this reaction can be controlled toremove only the less thermally stable compounds in the oil by employingS0 in solution in sulfuric acid containing from 2 to 10% S0 holding thetemperature at about 90 to 115 F. and employing rapid agitation toeffect proper contact. Under these conditions, the extent of thereaction can be controlled by varying the ratio of acid used to oiltreated. When using 30% by volume of acid containing 5% S0 we removeabout 45% of the oil, leaving 55% to be recovered after neutralizationand washing. Because the acid produces some oil soluble sulfonic acidswhich remain in the oil, serious emulsions are formed when the oil isneutralized and contacted with water. These are'broken by use of anemulsion breaking solvent, such as butyl alcohol or other light alcoholsup to 6 carbon atoms, glycol mono ethyl ether, etc. Secondary butylalcohol is very effective and can be recovered easily in the form of itsaqueous phase containing about 72% alcohol and 28% water.

We prefer to control the S0 treatment to remove from 40% to 50% byvolume of the linear alkylate fraction which has been previouslydistilled to meet the required narrow boiling range for our powertransmission oil. Surprisingly enough, the S0 reaction has little, ifany, effect on the vaporization characteristics of the oil, from whichit appears that the less stable hydrocarbon constituents are evenlydistributed throughout the molecular weight range of the alkylate. Thisis indicated by the ASTM distillation of the oils as shown in thefollowing table. Dealkylation taking place in the S0 reaction appears tobe followed by sulfonation of the de-alkylation products, both aromaticand paraffinic. There is a significant increase in both the flash pointand viscosity index following the S0 reaction.

Alkylate after Alkylate S03 reaotion stock 56% yield Gravity, API 28. 832. 0

Viscosity, F. cs 20. 47 20. 98

Viscosity, 210 F. cs 3. 81 3.92

Viscosity index 74 82 Flash point, 410 430 Pour point, F 75 80 Anilinepoint; 123. 4

Color, ASTM (D1500) l. 0 Distillation ASTM:

Initial F 662 664 1 Water white.

Where unusually high thermal stability is not required, we can reducethe severity of the S0 treatment and supplement it with a claytreatment. For this purpose, we can employ an acid treated bentonite ormontmorillonite clay, for example, Filtrol, Grade 13 which has an acidnumber of 16 mg. KOH equivalent per gram. Clays having an acid number inthe range of about 5 to 20 are suitable. The clay treatment is carriedout by contacting or percolating at 300-500 F. in an inert atmosphere.Air can be conveniently excluded with a C0 or nitrogen blanket. The claytreatment may precede or follow the S0 treatment. If S0 precedes theclay, it is possible to omit the steps of neutralization and washingfollowing the S0 reaction. In either case, it is preferred to strip theoil with steam at about 500 F. to remove de-alkylation products or anylow boiling substances which would adversely affect the flash point ofthe finished oil. The stripped oil is then given a final clay treatmentor polish with a neutral clay (less than 2 acid value) to absorb colorand remove a trace of acid derivatives left by the S0 treatment. Atemperature of 200300 F. is satisfactory for this operation.

Extraction of the oil with selective solvents such as furfural, phenol,dichlor ethyl ether, etc., can be employed to improve color and increaseviscosity index. We prefer to employ such solvent refining as apreliminary to $0 treating. Thus, We can extract 30 to 50 percent of theoil with furfural, preferably in stages, then contact the partiallyrefined oil with S0 to give a yield overall of 35 to 65% in a typicaloperation.

FIIG. 2 of the drawings is a flow diagram of the S0 treating operationapplied to the linear alklate oil of curve 5, FIG. 1. It will be seenthat, in this case, a charge of 68 gallons yielded 38 gallons of treatedoil or 56% of the oil charged. Time of stripping-1 to 2 hours.

, Another example of the eifect of S treatment of the alkylate oil isfurther illustrated by the following data:

1 Below 80 F.

The 80;, treated sample had received 30% (volume) of H SO containing 5%S0 followed by neutralization and washing. The untreated oil boiledwithin a narrow range, 90% within 46 F., indicating that the synihetichydrocarbons of which it is composed have a relatively uniform molecularweight and type.

We believe the increase in API gravity obtained by the S0 treatment canbe the effect of removing naphthalene derivatives and polyphenylcompounds, particularly diphenyl alkanes, contained in the heavyalkylate. We prefer to fractionate the oil, either before or aftersolvent extraction, to a boiling range of about 675 to 750 F. Stillcloser fractionation will provide an oil boiling in the range of 700 to725 F. with still higher flash point. However, it is often desirable tomerely strip the oil with steam or other inert gas after the chemicaltreatment to obtain the flash point.

The S0 treated oil of the foregoing example was compounded to consist of96.0% oil, 1.0% tricresyl phosphate, 0.5% Parabar 441 (alkylated phenoloxidation in- .hibitor sold by Enjay Chemical Company), and 2.5%

Paratone N (polybutene concentrate sold by Enjay Chemical Company). Thefinished oil had the following physical properties:

Gravity, API at 60 F. 31.5 Pounds per gallon 7.228 Viscosity at -40 F.,cs. 9,263 Viscosity at 100 F., cs 25.66 Viscosity at 210 F., cs 4.68Viscosity index 110 Flash point, COC, F. 4.15 Fire point, COC, F. 450Pour point, F. 80 Color, NPA 1 The compounded oil was tested for thermalstability by heating a 100 ml. sample in a glass tube under nitrogen for72 hours at 500 F. with no significant change in appearance orproperties. The compounded oil was also subjected to an extremely severetest by a leading manufacturer of supersonic aircraft. The oil waspumped at 4,000 p.s.i. pressure in a simulated supersonic aircrafthydraulic system at 425 F. for 1,500 hours. The pump, servo mechanismsand other parts of the system in contact with the oil were judged to bein excellent operating condition at the end of the test. The oil afterthis extremely severe test showed no significant change in propertiesother than a slight darkening in color. All other hydraulic fluids(including hydrocarbon, silicone, silicate ester, and polyol ester basedfluids) failed this performance test in unsatisfactorily short periodsranging from 5 to 200 hours. The superior performance of our linearalkylate oil under these severe conditions, which must be met to satisfythe requirements for 1,800-2,000 miles per hour airplanes, constitutes anotable contribution toward the practical operation of such aircraft inboth military and civilian use.

In addition to additives shown in the foregoing examples, otheroxidation inhibitors, wear reducing agents, and viscosity indeximprovers may be used in our oil in minor amounts where specialconditions require them. Also our oil may be blended with compatiblefluids such as refined natural petroleum oils, diesters such as di-2-ethyl hexyl sebacate, polyol esters such as tri-methylol propanepelargonate or pentaerythritol heptanoate, polyphenyl ethers, phosphateesters such as hexyl dicresyl phosphate, silicate esters, siloxanes andsilicones.

The addition of a small amount of shear stable, thermally stable polymerappears especially beneficial in reducing leaking with certain designsof mechanical seals. The addition of 2.5% of the polybutene concentratesold under the name of Paratone N made a marked improvement in sealleakage in rigorous high pressure recycling tests. Other oil solublepolymer viscosity index improvers having molecular weights in the rangeof 10,000 to 20,000 can be employed in amounts of 1 to 5 percent byweight.

Having thus described our invention, what we claim is:

1. The process of making power transmission oils having high flashpoints above 400 F. and low pour points below 70 F. wherein a normalparaflin hydrocarbon of 10 to 13 carbon atoms and 140 to 170 molecularweight is chlorinated to produce a mixture of monochlor and polychlorparaffins wherein at least 70% is monochlor paraffin, alkylating benzenewith said chlor paraflins in the presence of 2-10 percent of aluminumchloride alkylation catalyst and excess benzene in the mo] ratio of 2-5mols benzene per mol of chlor paraflin to maximize formation of monoalkyl benzene hydrocarbons, distilling the alkylation product to removea major fraction consisting of mono alkyl benzenes, and continuing thedistillation to recover a power transmission oil fraction boilingsubstantially entirely within the range of 650 to 760 F., whereupon thesaid power transmission oil fraction is treated at about to F. with thesulfur trioxide in solution in sulfuric acid at a concentration of about2-10 percent to remove polyphenyl compounds and naphthalene derivatives,washed and neutralized.

2. The process of claim 1 wherein the said power transmission oilfraction is treated with a selective solvent to remove polyphenylcompounds and naphthalene derivatives before sulfur trioxide treating.

3. The process of claim 1 wherein the said S0 treated oil is decolorizedby contacting with adsorbent earth.

4. The power transmission oil made by the process of claim 1 containingin solution therein from 0.1 to 1% of an antioxidant consisting of aphenolic compound.

5. The power transmission oil made by the process of claim 1 containingin solution therein from 1 to 5% of an oil soluble polymer viscosityindex improver having a molecular weight of 10,000 to 20,000.

6. A synthetic, functional hydrocarbon oil consisting essentially ofaromatic rings substituted with linear paraffin side chains, made byalkylating benzene with a monochlorinated normal hydrocarbon of theparaflin series having about 10 to 13 carbon atoms by the action ofaluminum chloride catalyst in the amount of 2 to 10 percent of theweight of the chlor parafiin, and distilling the resulting alkylationproduct to remove undesired lower boiling alkylates boiling below about650 F., and higher boiling alkylates boiling above about 760 F., saidoil having the following characteristics:

said oil distilling substantially entirely within the range of 650 to760 F. and consisting essentially of the following hydrocarbons:

Percent Dialkyl benzenes 40-60 Dialkyl tetralin 15-25 Dialkyl diphenyl1015 Unidentified hydrocarbons 10-15 7. The process of making powertransmission oils having high flash points above 400 F. and low pourpoints below 70 F. wherein a normal parafiin hydrocarbon of 10 to 13carbon atoms and 140 to 170 molecular weight is chlorinated to produce amixture of monochlor and polychlor paraflins wherein at least 70% ismonochlor paraflin, alkylating benzene with said chlor parafiins in thepresence of 2-10 percent of aluminum chloride alkylation catalyst andexcess benzene in the mol ratio of 2-5 mols benzene per mol of chlorparafiin to maximize formation of mono alkyl benzene hydrocarbons,distilling the alkylation product to remove a major fraction consistingof mono alkyl benzenes, and continuing the distillation to recover apower transmission oil fraction boiling substantially entirely withinthe range of 650 to 760 F., whereupon the said power transmission oilfraction is treated in an inert atmosphere with an acidic adsorbentearth at 300-500 F., then cooled and treated References Cited UNITEDSTATES PATENTS 3/1965 Pappas et al. 252-59 X 9/1968 Feighner et a1.260-671 LEON D. ROSDOL, Primary Examiner D. SILVERSTEIN, AssistantExaminer US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,544,472 December 1 Ulric B. Bray et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 5, "a

corporation of California" should read a limited partners of CaliforniaColumn 1, line 71, "defining" should read refining Column 6, lines 30 to40, the second column c figures should appear as shown below:

Column 8, line 30, cancel "the". Column 10, line 4, "adbsorbent shouldread adsorbent Signed and sealed this 27th day of April 1971.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. WILLIAM E SCHUYLER, J Attesting OfficerCommissioner of Patent

